The present invention relates to an electrically changeable (rewritable) logic integrated circuit with security protection function.
There has been a strong demand for rewritable logic integrated circuits suitable for a shorter term for logic integrated circuit development or modification after shipment. The logic integrated circuits are freely rewritable to constitute circuits with completely different logic functions. And, these logic integrated circuits have been used for communications equipment such as mobile phones, add-on boards of computers, video-game apparatus and Karaoke-apparatus, etc.
On the other hand, virus programs have been spread all over the world to rewrite, without authorization, programs or data stored in rewitable storage media for computers, such as hard disks, floppy discs, BIOS flush memories. The virus programs are infected from one to other computers through communications media or floppy discs, etc. These virus programs have given extensive damage to computer users because some of them destroy the data or programs to cause malfunction of computers.
In order to protect computers from the virus programs, vaccine programs have been widely used as a means for preventing infection of the virus programs or heal the damaged data or program.
For example, Japanese patent Laid-Open No. 8(1996)-179942 describes a computer system with virus program detection function. Further, Japanese patent Laid-Open No. 8(1996)-22390 describes a system for judging whether data or software of a computer is rewritten.
A semiconductor device provided with the security protection function is disclosed in Japanese Patent Laid-Open No. 4(1992)-232588. Particularly, this device is provided with the security protection function for IC cards. The semiconductor device includes a ROM for storing a software for basic control, etc., an EEPROM for storing a program for ciphering and a ciphering key, a RAM for storing identification number of a manufacturer, etc., and a CPU for controlling the ciphering function.
Further, Japanese Patent Laid-Open No. 4(1992)-11420 discloses a one-chip microcomputer provided with a non-volatile memory for storing ID data to be ciphered, a ciphering circuit for ciphering the ID data, a control circuit, etc.
Further, Japanese Patent Laid-Open No. 63(1988)-293637 discloses a one-chip microcomputer provided with a non-volatile memory (ROM) for storing ciphered program and ID data, a volatile memory (RAM) for storing keys for ciphering and deciphering, and a rewritable memory (EEPROM) for storing data ciphered by the ciphering key.
Since the rewritable logic integrated circuits have been used in fields where security protection is required, the same as computers, there is a demand for logic protection function for such rewritable logic integrated circuits against virus programs.
The methods against virus programs described, for example, in Japanese patent Laid-Open Nos. 8(1996)-179942 and -22390 are used for data or software of a computer. However, these cannot be used for logic of rewritable logic integrated circuits. There have been no way to protect logic of rewritable logic integrated circuits from being rewritten without authorization.
Further, in the semiconductor device provided with the security protection function, the EEPROMs of these semiconductor device have relatively large area required for one-bit data, there exists a problem in that a high integration is difficult to achieve. In addition, in these devices, since the secret data are ciphered and deciphered by processing programs by use of a CPU, there exist other problems in that a relatively long time is required to output data and further in that the CPU cannot execute another processing while the data are being output. This device may also be infected by virus to destroy the stored data, thus causing malfunction.
As described above, in the semiconductor devices provided with a security protection function, there exists a problem in that a high integration is difficult and thereby the device cannot be manufactured at a low cost. In addition, the semiconductor devices involve such a problem that the stored data cannot be output at high speed and further another different processing cannot be executed by the arithmetic unit while the data are being output. Further, a normal operation cannot be secured against virus programs.